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The current research examined how people form context-based trait impressions and why some of these impressions are stronger than others. This research drew from principles of attention theory (Kruschke, 1996, 2001) in order to account for the processes underlying impression formation in context. According to attention theory, the traits expressed by an individual target person in a rarely occurring context should be more strongly associated with that context than the traits expressed in a commonly occurring context are associated with the common context. That is, people form stronger impressions of others' behavior in rare compared to common contexts. Four experiments provide support for these predictions. The current study is one of the first to examine the cognitive mechanisms by which perceivers form trait impressions of individuals across different contexts and to explain why some of these impressions are stronger than others. Implications of the nature of these impression formation processes are discussed. [ABSTRACT FROM AUTHOR]

All the well-defined DNA-packaging motors of the dsDNA viruses contain one pair of nonstructural DNA-packaging enzymes. Studies on the mechanism of virus DNA packaging have been seriously hampered by their insolubility. Phi29’s DNA-packaging enzyme, gp16, is also hydrophobic, insoluble, and self-aggregating. This article describes approaches to obtain affinity-purified, soluble, and highly active native gp16 with the aid of polyethylene glycol or acetone. The specific activity of this native gp16 was increased 3400-fold when compared with the traditional method. This unique approach made the ATP–gp16 interaction study feasible. Gp16 binds strongly to ATP, binds to ADP with a lower efficiency, and binds very weakly to AMP. The order of gp16-binding efficiency to the four ribonucleotides is, from high to low, ATP, GTP, CTP, and UTP. The ATP concentration level required to produce 50% of maximum virus yield exhibited during in vitro phi29 assembly is around 45 μM, which is close to the gp16 and ATP dissociation constant of 65 μM. Mutation studies revealed that changing only one conserved amino acid, whether R17, G24, G27, G29, K30, or I39, in the predicted Walker-A ATP motif of gp16 caused ATP hydrolysis and viral assembly to cease, while such mutation did not affect gp16’s binding to ATP. However, mutation on amino acids G248 and D256 did not affect the function of gp16 in DNA packaging. [Copyright &y& Elsevier]